The invention relates to a lens for a backlight module and a light emitting diode and, more particularly, to a dish lens for a direct type backlight module and a light emitting diode.
The arrangement of an LED for small backlight module of an LCD has recently been developed from side to an array arrangement suitable for a larger direct backlight module, which must blur the outline of the LED array to normalize the luminance of the LCD. Increasing the distance between the light source and the diffuser or the thickness and the haze of a diffuser can solve the above problem.
Referring to FIG. 1, a backlight module 1 comprises a diffuser 11, a reflective sheet 13, and a point light unit 14. The point light unit 14 is disposed between the diffuser 11 and the reflective sheet 13. The light emitted from the point light unit is reflected by the reflective sheet 13 and passes through the diffuser 11 to blur the outline of the point light unit 14.
Because the luminance between the point light unit 14 and reflective sheet 13 of the conventional backlight module 1 are different, the brightness of the display is not uniform. Although increasing the distance d between the point light unit 14 and the diffuser 11 solves the problem, the thickness of the backlight module increases the profile of the display.
Referring to FIG. 2, increasing a diffuser 11a also can solve the above problem. The diffuser 11a overlaps diffuser 11, increasing the thickness and the haze of the diffusers 11, 11a, blurring the outline of the tubes 14. The diffuser 11a not only increases costs but also the profile of the backlight module 1. As well, overlapping the diffusers 11, 11a decreases the utility rate of the light source. Increasing of point light units 14 results in increased costs.
FIG. 3 shows an embodiment disclosed in U.S. Pat. No. 6,679,621, SIDE EMITTING LED AND LENS, in which lens 15 comprises a funnel-shaped first element 151, and a second element 152 located under the lens 15. The first element 151 comprises a reflective surface 153 and a first light-refracting surface 154. The second element 152 comprises a curved second light-refracting surface 155 and a curved bottom surface 156. When an LED is put on point L, a first light beam 17 emitted from the LED passes through the bottom surface 156 to enter the lens 15 and is reflected by the reflective surface 153 through the first light-refracting surface 154, exiting the lens 15. A second light beam 18 emitted from an LED passes through the bottom surface 156 to the lens 15, and is refracted by the second element 152 to leave the lens 15. Light is reflected and refracted to increase luminance on sides of the lens 15. Because reflective sheet 16 is curved, thickness of the backlight module increases, while luminance is still not uniform.